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2nd grade math - addition & subtraction word problems with unknowns

Clip 3/11: Number Talk Part 2


In the second half of the number talk, Mia Buljan’s student Natalie describes her strategy for solving the two-digit addition problem. Mia connects Natalie’s response to her students’ use of tools, as students use ten sticks and cubes on their trays to build tens and work with ones.

Mia asks her students to work with Natalie’s way, grouping tens and ones to build numbers. Mia asks her students to talk in pairs and compare Natalie’s way of solving to other students’ ways, working with the sentence stem “I think it’s like ______’s way because______.”

One student says, “She used the counting way in her head, and then used Anthony’s way of putting the tens and ones together.”

Finally, a student with a very different answer shares her thinking, and it becomes clear that she was counting on from 32 and lost track of where she was in her counting.

Teacher Commentary

By this time of the year, “counting on” with ones can introduce greater possibility of error, as opposed to counting by tens. I ask the student which student’s strategy she will use in the future, and suggest that in the future these two students work together and talk through their thinking.